South Dakota. 

Geological and Natural History Survey 

VERMILION 

FREEMAN WARD, State Geologist 


CIRCULAR NO. 4 


The Possibilities of Oil and Gas 


in Harding County 





) * 


October, 1918 


Monograph. 





Introductory 

Interest in oil and gas in this state still runs high despite the lack of 
any big finds to date. Considerable inquiry has been made concerning 
the N. W. part of the state. To meet this demand the past field season 
was devoted to a study of the region. 

This circular records the cinef facts that have been determined to 
date, and presents the theoretical side of the question in a general way. 
Further field work is necessary before anything more positive can be 
said. The problem will probably never be entirely settled until, in addi¬ 
tion to the field work, a few deep holes are put down 

No attempt is made to give references to the literature or quote au¬ 
thorities. Thorough and complete treatment of the problem is reserved 
for a later Bullet n. 

Harding County is in the extreme N. W. corner of the state. 

Much that is stated herein can be applied equally well to other parts 
of N. W. South Dakota outside of Harding County. 


General Geology 

Areal Geology. 

The rocks of this region are all of sedimentary origin. Probably 
four-fifths of the county is covered by the Lance. This consists essen¬ 
tially of clays and shale with local beds of sandstone. Beds of lignite 


Geological Section for Northwestern South Dakota 


Formations 


Thickness (in feet) 
Max. Min. Ax. 




Arikaree 

225 

0 

125 

Tertiary 


White River 

140 

0 

75 



Ft. Union 

425 

0 

150 

Tertiary? 

Cretaceous? 

0) 

Cannonball Marine 

100 

0 

50 

o 

C 

03 

Ludlow Lignitic 

350 

0 

300 


*-5 

Lower 

425 

0 

350 



Fox Hills 

100 

25 

65 



Pierre 

•i i 

1500 

1300 

1400 

GO 

3 

o 


Niobrara 

200 

150 

175 

o 

V 

Cti 

s 

Carlile 

800 

600 

700 

o> 

u 

U 

© 

s 

CD 

Greenhorn 

50 

25 

35 


CQ 

Graneros 

1200 

800 

1000 



Dakota 

120 

40 

80 







■SRARV OF CON 


i 14 0 1934 


V * i 4 I ft 


V [ * t \ : £ 



























































































TN^U 


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are also common in parts of this formation. None of the strata are widely 
persistent; rather, variation is the rule both vertically and horizontally. 

In the N. E. part of the County and further west in the Cave Hills 
and Table Mountain the surface material is Ft. Union. In the Slim 
Buttes and Short Pine Hills—S. E. and S. W. parts of the County respect¬ 
ively—the Arikaree and White River occur. The first two formations are 
made up predominantly of sandstone. The latter is chiefly clays. 

There is a small area of Fox Hills (sandstone) in me N. W. part of 
the County. And along the extreme southern part of the County Fox 
Hills again is present together with slightly larger tract of Pierre (shale). 

No attempt is here made to give a detailed description of these for¬ 
mations. 

Columnar Section. 

Below these surface formations it is known that other formations 
occur. In the table (page 2) is given the typical geological section for 
N. W. S. Dak. The youngest formation is placed at the top, the oldest 
at the bottom, and the others in orderly sequence between. 

No attempt is made to list the Comanchian or older rocks, for they 
have little bearing on the problem. 


Sructure. 


The term structure refers to the attitude or position of the beds. 
The type of structure most favorable for the occurrence of oil and gas is 
the anticline. The importance of structure in oil and gas investigation 
calls for a careful consideration of this subject in reference to the area 
in question. 

The Plains Region.—Throughout the Plains region, of which Harding 
County is a part, the beds are essentially flat. If they were absolutely 
and uniformly flat there would be little to say further. But such is not 
the case. 

The largest structural feature—as marked by the position of the Da¬ 
kota sandstone—is an immense synclinorium, some 250 miles across and 
500 miles long. This trends N. W. and S. E., reaching from Saskatoon, 
Canada, down through eastern Montana and western N. Dak., and into 
northern S. Dak. 

Of lesser dimensions but still a major feature is the Black Hills up¬ 
lift, whose main axis also trends N. W. and S. E. 

On the northern flanks of the Black Hills, in southern Butte County 
and N. E. Wyoming, distinct anticlinal structures are present with a N. W. 
and S. E. trend. In eastern Montana a well marked anticline—the Glen¬ 
dive or Cedar Creek anticline—again trends N. W. and S. E. A syncline 
parallels it on the S. W., followed in turn by another anticline. Both of 
these, however, are not as well marked as the Glendive structure. 

Anticlines trending N. W. and S. E. occur also in N. Central Montana. 

In northern N. Dak. another low but distinctly marked anticline is 
known—this trends north and south. 

It seems clear, then, that the general flatness of the Plains strata is 
relieved by the presence of open folds, which almost uniformly trend in 
some N. W. and S. E. direction, less commonly north and south. These are 
known in northeast Wyoming, in eastern Montana and in N. Dak. 

Harding County.—One of the important parts of the problem is to de¬ 
termine how far the local structure of Harding County responds to the 
larger structure of the region. 

The N. E. part of the County is considered by the Federal Survey to 
have the structure of a basin-like syncline whose axis is further east in 
Perkins County. The dips are very low,—7 to 65 feet per mile. It is pos¬ 
sible that careful field work may bring to light some local flexures, though 
no strongly marked anticlines with dips over 5 degrees can be expected. 
In fact, an examination of the Cave Hills area shows that the North Cave 




Hills are on an anticline whose axis is approximately arong their S. W~ 
edge and which trends N. W. and S. E.: while the South Cave Hills have- 
a position in the contiguous syncline. The dips in eacn case are low, 
being not over 50 feet per mile. 

The Glendive anticline trending S. E. cuts across the S. W. corner of 
N. Dak. and is known to enter S. Dak. in a modified form in Harding 
County, Range 2 east. It has lower dips and is less plainly marked than 
in Montana. Just how far it reaches into the county can only be deter¬ 
mined by further detailed field work. 

In the S. W. part of the County just south of the West Short Pine 
Hills there has been reported another low arch again trending N. W. and 
S. E. 

The presence of these several low flexures suggests tnat others will 
be found upon close inspection. 

Two weeks’ time was spent in a restricted area in the N. W. part of 
the County,—Towns 21 and 22 N., Range 1 E—where the rock exposures 
were fairly good. Plane table and level were used. 

It is clear from this work that in this particular locality the structure 
does respond to the larger feature of the region, for the strata in general 
strike N. W. and S. E. Furthermore, a fairly well-marked doinnal anti¬ 
cline was located in Section 8, T. 21 N., R. 1 E. The dips are again low, 
but are considerably higher than those in the east part of the County. 
The maximum dip observed was 3 degrees. 

It is believed that further work done with the proper care will bring 
to light other anticlines in the County, some of whicn may be more 
strongly marked than those so far discovered. Only a little has been ac¬ 
complished sb far. Most of the County has yet to receive this close 
scrutiny. 

Tertiary vs. Cretaceous Structure.—There still remains another phase 
of the structural problem to consider: viz,—does tne Dance-Tertiary 
structure of the surface faithfully reflect the Cretaceous sructure below? 
This is critical bcause the oil and gas—if present at all—are to be expect¬ 
ed in the Cretaceous rather than the other. 

The date of the major deformation—such as the main Black Hills 
uplift and the formation of other large folds—has usually been given as 
the close of the Cretaceous. 

The Lance-Tertiary was then deposited, probably following a period 
of erosion. This means that the folds now seen are of a still later date. 
It means further, that well-marked folds in he Cretaceous may now be 
covered by flat-lying or but slightly deformed Lance-Tertiary beds. 
Some deformation is known to have occurred also in Tertiary time. It is 
possible, too, that the deformation may have occurred so late in Tertiary 
time that the oil and gas previously accumulated in older structures has 
not had time or opportuniy to get into the newer structures. 

While some doubt may legitimately exist in regard to these matters, 
probably the most satisfactory answer to this question—at least for this 
N. W. region—is the condition of the Glendive anticline. This is a well- 
marked anticline; it has the prevailing trend; the Lance-Tertiary beds 
and the Cretaceous below are deformed as a unit; and tfie field is a pro¬ 
ductive one. 

It can be reasonably concluded that in this region the surface Lance- 
Tertiary structures are a safe index of the deeper structure. 

Faults.—In so far as the County has been examined It can be said 
that there is a general absence of faults. The occasional fault encoun¬ 
tered is local and of small dimensions. 


Surface Evidence of Oil and Gas 

No oil seepages or scums, no gas springs, no asphaltic substance, etc., 
have been found by this Survey. A number of cases of scums have been 



reported. These have been examined in so far as that was possible and 
none of them have been indicative of oil or gas. As far as is known there 
is no authentic case of surface evidence of oil or gas in the County. 

The entire absence of surface indications of oil and gas does not nec¬ 
essarily mean an entire absence of those substances deeper down. In 
fact, there is every reason why they should not reach me surface—as¬ 
suming that they are present below—for the oil and gas horizons of this 
region are in the Cr taceous and the thick cover of dense, impervious 
Pierre Shale would naturally prevent any upward escape. Cracks and 
openings in the overlying Pierre might let the oil and gas work towards 
the surface, but there seems to be a general absence of such fractures. 

The absence of surface indications is an entirely negative piece of 
evidence. 


Other Evidence of Oil and Gas 

Relation to Wyoming and Montana Fields, 

The belief that oil or gas may exist below the surface in this County 
has arisen because in the neighboring states of Wyoming and Montana 
both oil and gas have been found. The value of this relation depends on 
the distance from the nearest producing fields, the correct correlation and 
possible variation of the same strata in the given distance, and other 
factors. 

It must not be forgotten that this is a pure assumption, and it 
must not be accepted as valid without due consideration of what it 
involves. 

Wyoming.—The nearest productive field in Wyoming is the Moorcroft 
field in the N. E. part of the state. It is 70 miles from the nearest part 
(S. W. corner) of Harding county. It has never reached quantity pro¬ 
duction and at the present time it is rated as non-productive. The chief 
oil horizon is the Graneros. There are other anticlines in Wyoming 
nearer to S. Dak. These are now being explored. 

Until oil or gas is struck in commercial quantity in the N. E. corner 
of Wyoming, the relation between Harding county and tne Wyoming oil 
field can only be considered suggestive: it should cause no excitement 
nor create any strong hopes of success. 

Montana.—The nearest productive field in Montana is tne Baker field, 
which is 35 miles from the nearest part (N. W. corner) of Harding County. 
This field is already productive of gas (no oil yet) on a commercial scale 
and bids fair to increase in importance very decidedly. It is located on 
the Glendive anticline already mentioned. The gas horizon is a sandstone 
bed in the Pierre. 

The Baker field is an important one. It is not an extreme distance 
from Harding County. The anticline on which the field is located reaches 
into Harding County. All this does warrant some assumption that gas 
(and possibly oil) may be found in the County either on the main anti¬ 
cline itself or some of the smaller ones adjoining, providing any other 
factors do not interfere. 

Correlation of Strata. 

Another factor in the problem must be considered before the as¬ 
sumption can be carried any further. The oil and gas horizons in Wy¬ 
oming and Montana are in the Cretaceous. Are we sure that these same 
strata are present below the surface in Harding County? 

Since the Cretaceous as a whole—Pierre, Dakota, Benton, etc.,—is 
known to be wide spread, has been encountered in all directions away 
from Harding County, and indeed is present in part along the edges of 
t?he County itself, we feel sure that it must underlie the whole County. 

But this fact does not satisfy the whole condition of correlation. The 
variations that are known to be developed in Wyo. and Mont, may or may 



not be present in Harding County, and these variations are apt to be 
critical. For instance,—the Pierre, which is known to be in all three 
states, and in Harding County, has a variation of importance. In all of 
S. Dak. where it is well exposed and known from top to bottom, it is uni¬ 
formly and persistently a shale. This is true in the type locality—central 
part of the state—and in the region north of the Black Hills, in Butte 
County. Further west sandy beds appear in this shale. The gas horizon 
in the Baker field is a sandstone bed in the Pierre. In central Wyo. the 
Parkman, Teapot, and Shannon sandstone are members o£ trie Pierre for¬ 
mation. Similarly the Benton equivalents in Wyo. are the prominent and 
productive Frontier and Wall Creek sandstones. 

It is known that these sandy members thicken toward the west and 
thin towards the east: they are known to be prominent in centrai Wyo. and 
eastern Mont, and absent in central and western S. Dak. At just what 
po.nt in western S. Dak. or eastern Mont, and Wyo. they begin to be ef¬ 
fective is not known,—and this is a critical point in the problem. If it 
can be shown that the Cretaceous along the western edge of Harding 
County is the same as it is 100 miles east, then there is little use in being 
concerned about oil in S. Dak.,—and vice versa. The Pierre in Butte 
County has some porous limestone lenses. It is barely possible that 
these may act as reservoirs of oil and gas though little can be expected 
from them in this capacity. 

The only way to decide whether the Cretaceous of Harding County 
does or does not contain these important sandstone members is by trial. A 
deep hole—preferably several holes—must be put down, abundant sam¬ 
ples taken, a careful log kept, and all the data turned over to someone 
competent to interpret it. 


Field Work 

As has been intimated, a great deal of work needs to be done in the 
field before the exact structural conditions are known throughout the . 
County. This field work must be careful and detailed if it is to yield 
results. 

The difficulties of the field are several. 

In the first place there are rather large tracts which have a nearly 
continuous sod cover with scarcely any outcrops. The desired data are 
not visible. Wells are so few in number, so shallow, and so widely 
spaced that they are of little help. 

Another difficulty is the character of the rocks themselves even when 
well exposed. Instead of the well marked continuous Cretaceous beds, 
such as occur close around the Black Hills, or in central Wyoming for 
instance, there are the poorly marked, lense-like Lance-Tertiary beds. 
This makes the finding and tracing of index beds a much more difficult 
matter. 

A third difficulty lies in the fact that the dips are low. This requires 
careful work with a good level rather than approximate work with hand 
level and clinometer. 

Finally, there are no satisfactory base maps of the County. A good, 
large-scale topographic map would be a tremendous help. 

Because of these difficulties field work must progress slowly. 


Depth to Productive Horizons 

If we accept the assumption that oil or gas, or both, exist underneath 
this area, then, the probable depths to the productive strata should be cal¬ 
culated. 

There are four horizons that need to be considered in this connection: 

1.—The Pierre. In the Baker field gas is struck approximately 1100 
feet below the top of this formation. 




2. —Greenhorn. The important Frontier in central Wyo. is in an 
equivalent position. It is very doubtful whether there is a single sand¬ 
stone in the Greenhorn of this region but its depth can be calculated. 

3. —Graneros. The sandstone bed which in the Moorcroft field yields 
oil is in the lower part of the formation, in this region probably 750 feet 
below the top. 

4. —Dakota sandstone. 

The depth to each horizon depends on (a) the thickness of the 
formations (b) which particular formation is the surface material at a 
given locality, (c) how much of this surface formation has been removed 
by erosion. 

The table (page 2) gives the thicknesses of each formation in feet 
and arranged in three columns,—maximum, minimum, average. The 
Tertiary and Lance have zero in the minimum column. This is because 
they are the surface materials and in parts of the County have been re¬ 
moved by erosion and so are entirely lacking. 

Since no measurements have ever been made on the Cretaceous in 
the County the figures given are based on the nearest data in S. Dak., 

Mont., and N. Dak. As a consequence, they cannot be rated as absolutely 
accurate for this County. However, they must be reasonably near the 
truth. 

Naturally the depths' to the four horizons will vary, depending upon 
the locality chosen. A few illustrations will make this point clear. 

Suppose an estimate is to be made in T.^g'N., R. 2 E., Sect . jA'. The & *3 /2 
surface material here is the Fox Hdls. Some of it has been removed by 
erosion, how much is not known exactly. But probably 50 feet will fairly 
represent the probable thickness of that which remains. Horizon No. 1 
can be expected, then, after 50 feet of Fox Hills and 1100 feet of Pierre are 
are penetrated,—at a depth of 1150 feet from the surface. No. 2 will be 
reached after 50 feet of Fox Hills, 1400 feet of Pierre, 175 of Niobrara, 700 
feet of Carlile are penetrated, or 2325 feet from the sunace. The depth 
to No. 3 is ascertained by adding to this figure 35 feet of Greenhorn and 750 
feet of Graneros, which makes a total of 3110 feet. Similarly horizon No. 

4 will be reached at 3360 feet from the surface. 

If the dome located in Sect. 8, T. 21 N., R. 1 E., be the place chosen, 
the depths will be greater, for all the Fox Hills is present plus some of 

the lower Lance which is the surface material there. The center of this 
dome is in a badland tract which has been considerably dissected. It is 
difficult to tell -ow much has been removed by erosion, but it is believed 
that about 100 feet stil remains. Horizon No. 1 should be expected, then, 
after 100 feet of lower Lance, 65 feet of Fox Hills and 1100 feet of Pierre 
are penetrated, or a total of 1265 feet. Similarly No. 2 should be expected 
at 2440 feet, No. 3 at 3235 feet, and No. 4 at 3485 feet from the surface. 

If a hole is to be put down on the top of the Cave Hills the depths to 
the various horizons would have to be increased 800 to 1000 feet, for the 
surface is the Fort Union. Below it the Cannonball Marine member 
of the Lance is absent, but the Ludlow Lignitic and Lower members of 
the Lance are there in toto. 

Each locality in the County will have some modification of the 
figures given above. 


Summary 

1. —The absence of surface evidence is a negative argument; it neither 
supports nor refutes the belief that oil or gas is present. 

2. —The expectation of oil or gas in this area is based on its prox¬ 
imity to the productive Wyo. and Mont, fields. The actual distance from 
the former is considerable, but from the latter not excessive. The re¬ 
lation to the Wyoming field is only suggestive. But the Glendive anti¬ 
cline of Mont, is known to enter Harding County and so does give a 
reasonable hope for gas (and possibly oil) in S. Dak. 

3. —It is not known whether the Cretaceous strata Delow the area 
have beds porous enough to act as reservoirs even if oil or gas is pres¬ 
ent in the formations. Further west this favorable condition exists, fur¬ 
ther east it is known to be absent. 

4. —Field examination of the area shows structure paralleling the 
Glendive anticline, but with lower dips. A fairly well marked dome was 
found, which is one of the favorable locations for putting down a hole. 
Other anticlines will probably be found: they are more likely to occur in 
the western than in the eastern part of the County. 

5. —It is believed that there is a reasonable chance of striking gas 
(and possibly oil) in the County. The most favorable places for putting 
down holes are on the Glendive anticline itself and the smaller anticlines 
in the adjoining area, one of which has already been located. 

6. —But success cannot be promised. In an entirely new field the re¬ 
sults from the first hole are always the most difficult to predict. Until 
the first hole is put down the uncertainty is bound to be marked. If suc¬ 
cess is attained the pecuniary returns will be high. If no oil or gas is 
encountered the data from such a pioneer hole will always be a distinct 
contribution to scientific investigation, and in either case the information 
gained will aid tremenduously in guiding the placing of the next hole. 

FREEMAN WARD. 

Address all inquiries to the State Geologist, Vermilion, S. Dak. 


